Ablation electrode assemblies and methods for using same

ABSTRACT

Ablation electrode assemblies include an inner core member and an outer shell surrounding the inner core member. The inner core member and the outer shell define a space or separation region therebetween. The inner core member is constructed from a thermally insulative material having a reduced thermal conductivity. In an embodiment, the space is a sealed or evacuated region. In other embodiments, irrigation fluid flows within the space. The ablation electrode assembly further includes at least one thermal sensor in some embodiments. Methods for providing irrigation fluid during cardiac ablation of targeted tissue are disclosed that include calculating the energy delivered to irrigation fluid as it flows within the ablation electrode assembly through temperature measurement of the irrigation fluid. Pulsatile flow of irrigation fluid can be utilized in some embodiments of the disclosure.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The instant disclosure relates generally to ablation electrodeassemblies. In particular, the instant disclosure relates to ablationelectrode assemblies having an inner core member and an outer shellsurrounding the inner core member, wherein the inner core member and theouter shell define a space therebetween. In some embodiments, the spacecan comprise a vacuum region or evacuated region, and in otherembodiments the space can be configured for allowing the flow ofirrigation fluid. The instant disclosure further relates to methods ofusing ablation electrode assemblies, including methods for providingirrigation fluid during cardiac ablation of targeted tissue in a humanbody.

b. Background Art

Electrophysiology catheters are used in a variety of diagnostic and/ortherapeutic medical procedures to diagnose and/or correct conditionssuch as atrial arrhythmias, including for example, ectopic atrialtachycardia, atrial fibrillation, and atrial flutter. Arrhythmias cancreate a variety of conditions including irregular heart rates, loss ofsynchronous atrioventricular contractions and stasis of blood flow in achamber of a heart which can lead to a variety of symptomatic andasymptomatic ailments and even death.

A medical procedure in which an electrophysiology catheter is usedincludes a first diagnostic catheter deployed through a patient'svasculature to a patient's heart or a chamber or vein thereof. Anelectrophysiology catheter that carries one or more electrodes can beused for cardiac mapping or diagnosis, ablation and/or other therapydelivery modes, or both. Once at the intended site, treatment caninclude, for example, radio frequency (RF) ablation, cryoablation, laserablation, chemical ablation, high-intensity focused ultrasound-basedablation, microwave ablation. An electrophysiology catheter impartsablative energy to cardiac tissue to create one or more lesions in thecardiac tissue and oftentimes a contiguous or linear and transmurallesion. This lesion disrupts undesirable cardiac activation pathways andthereby limits, corrals, or prevents errant conduction signals that canform the basis for arrhythmias.

During RF ablation, local temperature elevation can result in coagulumformation on the ablation electrode, resulting in an impedance rise. Asthe impedance increases, more energy is passed through the portion ofthe electrode without coagulation, creating even higher localtemperatures and further increasing coagulum formation and theimpedance. Finally, enough blood coagulates onto the electrode that noenergy passes into the targeted tissue, thereby requiring the catheterto be removed from the vascular system, the electrode to be cleaned, andthe catheter to be repositioned within the cardiac system at the desiredlocation. Not only can this process be time consuming, but it can bedifficult to return to the previous location because of the reducedelectrical activity in the targeted tissue, which has been previouslyablated. Recent studies have also demonstrated the formation of aso-called soft thrombus in RF ablation. The formation of the softthrombus results from heat induced protein denaturation and aggregationand occurs independently of heparin concentration in serum. In addition,RF ablation can generate significant heat, which, if not controlled, canresult in excessive tissue damage, such as tissue charring, steam pop,and the like.

Accordingly, it can be desirable to monitor and/or control thetemperature of ablation electrode assemblies. It can also be desirableto use ablation electrode assemblies to provide irrigation fluid duringRF ablation. RF ablation catheters can be configured to providetemperature feedback during RF ablation via a thermal sensor such as athermocouple or thermistor. A temperature reading provided by a singlethermal sensor cannot accurately represent the temperature of theelectrode/tissue interface. This is because a portion of the electrodethat is in direct contact with the targeted tissue can have a highertemperature than the rest of the electrode that is being cooled by theblood flow. The orientation of the RF ablation catheter can affect theposition of the thermal sensor, and accordingly, can affect thetemperature reading provided by the thermal sensor. If the thermalsensor is in contact with the targeted tissue, the thermal sensor canprovide a certain temperature reading generally corresponding to thetemperature of the targeted tissue, but if the thermal sensor is not incontact with the targeted tissue, there will be a time lag before thethermal sensor provides a temperature reading generally corresponding tothe temperature of the targeted tissue, and due to the cooling effect ofthe blood flow, the thermal sensor can never approach the actualtemperature of the targeted tissue. In an effort to overcome the effectthat the orientation of the catheter can have on temperature sensing,multiple thermal sensors positioned at different locations on theelectrode can be used. For example and without limitation, the highestmeasured temperature can be used to represent the electrode/tissueinterface temperature. However, temperature measurements provided bymultiple thermal sensors cannot always accurately reflect thetemperature of the electrode/tissue interface (e.g., heat transferbetween the multiple thermal sensors can affect the temperature readingof each thermal sensor).

BRIEF SUMMARY OF THE INVENTION

It is desirable to be able to provide ablation electrode assemblies thatare configured to mitigate the effects of orientation of the RF ablationcatheter for monitoring the temperature of the ablation electrodeassemblies and/or targeted tissue, as well as to mitigate temperaturegradients (i.e., the directions and rates at which temperature changes)across electrodes. It is also desirable to interrupt and/or reduce heattransfer paths between multiple thermal sensors of the electrode,thereby improving the ability to distinguish between the temperaturereading associated with a thermal sensor that is proximate the lesionformed in the targeted tissue and the temperature reading associatedwith a thermal sensor that is proximate the circulating blood pool. Itis also desirable to have improved temperature correlation between theelectrode and tissue interface.

It is also desirable, in some embodiments, to segment the ablationelectrode and have an independent thermal sensor associated with eachsegment of the ablation electrode in order to offer even more completesegregation of the individual thermal sensors.

It is also desirable, in some embodiments, to include a mechanism toirrigate the ablation electrode assemblies and/or targeted areas in apatient's body with biocompatible fluids, such as saline solution, inorder to reduce charring and inhibit the formation of coagulum and/orsoft thrombus, as well as to enable deeper and/or greater volume lesionsas compared to conventional, non-irrigated catheters at identical powersettings. This can, in turn, enable greater energy delivery during RFablation. The flow of biocompatible fluids (i.e., irrigation fluids) canbe turbulent in order to provide an enveloping flow pattern adjacent tothe surface of the ablation electrode assemblies for mixing with,displacing, and/or diluting blood that can be in contact with theablation electrode assemblies in order to prevent stasis and theformation of coagulum. Pulsatile flow of irrigation fluids can helpprevent stagnation areas at the distal end of an electrode by increasingflow turbulence around the catheter. Pulsatile flow of irrigation fluidscan also improve correlation between the temperature of the electrodetip and the targeted tissue. The flow of irrigation fluids can bemodified based on information and feedback received during RF ablation.

It is also desirable, in some embodiments, to monitor a change in thetemperature of irrigation fluids during RF ablation in order to provideadditional information or feedback regarding energy delivery and/or thetemperature of the electrode and tissue interface. RF ablation can bemodified based on the information and feedback regarding energy deliveryand/or the temperature of the electrode and tissue interface. Operationin a temperature control mode can be at a set point above 55 degreesCelsius.

The instant disclosure relates to an ablation electrode assemblyincluding an inner core member having a distal end and proximal end andan outer shell surrounding the inner core member. The outer shell alsohas a distal end and a proximal end. The inner core member and outershell define a space (as used herein the term “space” includes, forexample, a volume or cavity or region). Herein, the term “annular” isused to describe the space; however, the configuration of the space canvary greatly and can be regular or irregular and can include supportmembers (e.g., flutes, bosses, posts, and the like) to maintainseparation and a useable space between the core and the shell. Thespacing between the core and the shell can vary, if desired, and thedistal end of the ablation electrode can be hemispherical, circular(e.g., the core and shell comprise a pair of concentric cylinders),rounded, geometrically-shaped, or the like. In an embodiment, theannular space can comprise a vacuum region or evacuated region. Theinner core member and outer shell can both be generally cylindrical inshape with a distal end that is generally hemispherical in shape. Theinner core member can comprise a thermal insulator having a reducedthermal conductivity, whereas the outer shell can comprise anelectrically conductive material. The inner core member can include atleast one channel configured to receive a thermal sensor, and theablation electrode assembly can include at least one thermal sensordisposed in the channel. The inner core member can include an outersurface, an inner surface defining an inner cavity, and a radiallyextending passageway that extends from the inner cavity to the outersurface of the inner core member. As used herein, the term “radiallyextending” means extending away from the longitudinal axis at any anglerelative to the longitudinal axis of the ablation electrode assembly.The inner core member can further include an axially extendingpassageway extending from an inner cavity of the inner core member tothe distal end of the inner core member. In an embodiment, the outershell can be scored with a plurality of axially extending grooves orslots to separate the outer shell into a plurality of segments. Each ofthe plurality of segments of the outer shell can have a correspondingthermal sensor.

The ablation electrode assembly can further include an irrigantdistribution element. The irrigation distribution element can beconfigured as a generally annular ring in accordance with an embodimentof the disclosure. The irrigation distribution element has a proximalend and a distal end. The distal end of the irrigant distributionelement can define a circumferential irrigation port between theirrigant distribution element and the inner core member.

In an embodiment of the disclosure, irrigation fluid can flow within atleast a portion of at least one of the inner core member and outershell. Irrigation fluid can flow from the inner cavity through theradially extending passageways in an embodiment with only proximaldelivery of irrigation fluid. Irrigation fluid can flow from the innercavity through the axially extending passageway in an embodiment withdistal delivery of irrigation fluid. Irrigation fluid can also flowthrough the space between the inner core member and outer shell. In anembodiment of the disclosure, irrigation fluid has a first flow rate ina first time period and a second flow rate in a second time period. Thefirst flow rate and the second flow rate can alternate and recur atintervals over time in accordance with an embodiment of the disclosure.In some embodiments, the second flow rate is greater than the first flowrate. For example and without limitation, the first flow rate can beapproximately less than or about two (2) milliliters per minute(ml/min.), and the second flow rate can be approximately 13 ml/min. Inother embodiments, the first flow rate is greater than the second flowrate and in yet other embodiments a single very low flow rate can beimplemented (at least vis-à-vis the prior known or typical irrigationfluid flow rates), for example, on the order of between about oneml/min. and less than about 13 ml/min. In some embodiments the first andsecond flow rates can be determined based on at least in part on atemperature measurement taken by a thermal sensor disposed on the innercore member. In some embodiments, the first and second flow rates can bedetermined based at least in part on an impedance measurement taken by apositioning electrode located on a catheter incorporating the ablationelectrode assembly. Accordingly, the first and second flow rates forirrigation fluid are based on feedback provided by the ablationelectrode assembly, including feedback regarding temperature and/orimpedance, for example and without limitation.

In an embodiment of the disclosure, a method for providing irrigationfluid during cardiac ablation of targeted tissue includes the step ofusing a catheter having a catheter shaft having a fluid lumen; and anelectrode assembly connected to the catheter shaft. The electrodeassembly includes an inner core member having a distal end and aproximal end and an outer shell having a distal end and a proximal end.The inner core member further includes an outer surface, an innersurface defining a cavity, and an axially extending passageway extendingfrom the cavity to the distal end of the inner core member. The outershell surrounds the inner core member, such that the inner core memberand the outer shell define a space. The method further includes thefollowing steps: delivering energy to the outer shell of the electrodeassembly; directing irrigation fluid from the fluid lumen to the cavityof the inner core member; allowing at least a first portion of theirrigation fluid from the cavity of the inner core member to flow in thespace between the inner core member and the outer shell; directing atleast the first portion of the irrigation fluid away from the spacebetween the inner core member and the outer shell; measuring a firsttemperature of at least the first portion of the irrigation fluid near afirst location where at least the first portion of the irrigation fluidenters the cavity of the inner core member; measuring a secondtemperature of at least the first portion of the irrigation fluid near asecond location where at least the first portion of the irrigation fluidexits the electrode assembly; calculating a temperature differentialvalue based at least in part on the first temperature and the secondtemperature; calculating a first value indicative of energy delivered toat least the first portion of the irrigation fluid as it flows from thefirst location to the second location based at least in part on thetemperature differential value; and calculating a second valueindicative of energy delivered to the targeted tissue based at least inpart on the first value indicative of energy delivered to at least thefirst portion of the irrigation fluid. In an embodiment of thedisclosure, the inner core member includes a first radially extendingpassageway that extends through the outer surface of the inner coremember. At least the first portion of the irrigation fluid can bedirected away from the space between the inner core member and the outershell to the first radially extending passageway in an embodiment. Inother embodiments, at least the first portion of the irrigation fluid isdirected away from the space between the inner core member and the outershell toward a proximal end of the catheter for elimination from thecatheter at a location that is remote from a patient. In an embodimentof the disclosure, the inner core member includes a second radiallyextending passageway that extends from the inner cavity to the outersurface of the inner core member.

The method for providing irrigation fluid during cardiac ablation oftargeted tissue further includes the steps of directing at least asecond portion of the irrigation fluid from the inner cavity of theinner core member directly to the second radially extending passageway.The first portion of the irrigation fluid can be separate from thesecond portion of the irrigation fluid. A flow rate of the first portionof the irrigation fluid can be independent of a flow rate of the secondportion of the irrigation fluid. A flow rate of the second portion ofthe irrigation fluid can be greater than a flow rate of the firstportion of the irrigation fluid with overall total fluid volumes muchlower than prior art or typically utilized in clinical practice,especially valuable for patients already suffering from fluid overload(e.g., patient having heart failure and the like). That is, overalltotal fluid volume can range from low single digits to about ten or somilliliters per minute while effectively reducing or eliminating charand coagulum and improving temperature correlation for precise controlof power to maintain a temperature during ablation procedures.

The outer shell of the electrode assembly can be electrically connectedto an ablation system including an ablation generator for generating anddelivering energy to the catheter. The energy generated and delivered tothe catheter from the ablation generator is based at least in part onthe highest temperature measurement from the plurality of thermalsensors in an embodiment of the disclosure. The energy generated anddelivered to the catheter from the ablation generator can be based atleast in part on the temperature differential value. The method forproviding irrigation fluid during cardiac ablation of targeted tissuecan further include the steps of correlating the temperaturedifferential value to a temperature of the targeted tissue anddetermining the temperature of the targeted tissue based at least inpart on the temperature differential value.

In an embodiment, another method for providing irrigation fluid duringcardiac ablation of targeted tissue can include the step of using acatheter comprising a catheter shaft having a fluid lumen; and anelectrode assembly connected to the catheter shaft. The electrodeassembly can comprise an inner core member having a distal end and aproximal end; and an outer shell surrounding the inner core member. Theinner core member and the outer shell can define a space. The method canfurther include the step of directing a pulsatile flow of irrigationfluid within at least a portion of at least one of the inner core memberand outer shell. The irrigation fluid can have a first flow rate in afirst time period and a second flow rate in a second time period. Thefirst flow rate and the second flow rate can alternate and recur atintervals over time. In some embodiments, the second flow rate isgreater than the first flow rate. For example and without limitation,the first flow rate can be approximately 2 ml/minute, and the secondflow rate can be approximately 13 ml/minute. In other embodiments, thefirst flow rate is greater than the second flow rate and, as notedabove, total flow rate (or volume delivered per unit of time) can beexceedingly low as compared to traditional irrigant flow rates (andvolumes). In some embodiments, the first and second flow rates forirrigation fluid can be based on feedback provided by the ablationelectrode assembly, including feedback regarding temperature and/orimpedance, for example and without limitation.

In an embodiment of the disclosure, a system for providing irrigationfluid during cardiac ablation of targeted tissue includes a cathetercomprising a catheter shaft having a fluid lumen and an electrodeassembly connected to the catheter shaft. The system further includes aplurality of thermal sensors disposed within the catheter; an ablationgenerator electrically connected to at least a portion of the electrodeassembly; an electronic control unit (ECU) operatively connected to eachof the plurality of thermal sensors; and a control system. The ECU isconfigured to: receive as an input data from the plurality of thermalsensors relating to temperature measurements of irrigation fluid,determine a temperature differential value responsive to the data,determine a first value indicative of energy delivered to at a least afirst portion of irrigation fluid, the first value responsive to thedata, determine a second value indicative of energy delivered to thetargeted tissue, the second value responsive to the data, and output thetemperature differential value, the first value, and the second value.The control system is configured to receive the temperature differentialvalue, the first value, and the second value and configured to controlenergy delivery of the ablation generator based at least in part on atleast one of the temperature differential value, the first value, andthe second value. The system can further include a sensor for measuringflow rates of irrigation fluid, and the ECU can be further configured toreceive as an input data from the sensor relating to flow rates ofirrigation fluid. The first value and the second value can be responsiveto the data from the sensor relating to flow rates of irrigation fluid.

The ECU can be configured to correlate the temperature differentialvalue to a temperature of the targeted tissue and store data relating tothe correlation between the temperature differential value and thetemperature of the targeted tissue. The control system can be configuredto retrieve data relating to the correlation between the temperaturedifferential value and the temperature of the targeted tissue andcontrol energy delivery to the ablation generator based at least in parton the temperature differential value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric partially transparent view of an ablationelectrode assembly in accordance with a first embodiment of thedisclosure.

FIG. 2 is a diagrammatic view of a system for performing one morediagnostic and/or therapeutic functions in association with cardiactissue.

FIG. 3 is a cross-sectional view of the ablation electrode assembly ofFIG. 1.

FIG. 4 is an isometric view of the ablation electrode assembly of FIG.1.

FIG. 5 is an isometric partially transparent view of an ablationelectrode assembly in accordance with a second embodiment of thedisclosure.

FIG. 6 is a cross-sectional view of the ablation electrode assembly ofFIG. 4.

FIG. 7 is an isometric partially transparent view of an ablationelectrode assembly in accordance with a third embodiment of thedisclosure.

FIG. 8 is a cross-sectional view of the ablation electrode assembly ofFIG. 7.

FIG. 9 is a flow diagram generally representing an exemplary method ofusing an ablation electrode assembly to control temperature duringcardiac ablation of targeted tissue in accordance with a firstembodiment of the disclosure.

FIG. 10 is an isometric partially transparent view of an ablationelectrode assembly in accordance with a fourth embodiment of thedisclosure.

FIG. 11 is a cross-sectional view of the ablation electrode assembly ofFIG. 7.

FIG. 12 is a flow diagram generally representing an exemplary method ofusing an ablation electrode assembly to control temperature duringcardiac ablation of targeted tissue in accordance with a secondembodiment of the disclosure.

FIG. 13 is a chart comparing the temperature of the distal end (i.e.,tip) of ablation electrode assemblies and the temperature of thetargeted tissue over time.

DETAILED DESCRIPTION OF THE DISCLOSURE

The instant disclosure generally relates to irrigated ablation electrodeassemblies. For purposes of this description, similar aspects among thevarious embodiments described herein will be referred to by similarreference numbers. As will be appreciated, however, the structure of thevarious aspects can be different among the various embodiments.

An embodiment of an ablation electrode assembly 10 is generally shown inFIG. 1. Referring now to FIG. 2, the ablation electrode assembly 10 cancomprise part of an irrigated catheter system 11 for examination,diagnosis, and/or treatment of internal body tissues (e.g., targetedtissue areas 13). In an exemplary embodiment, the irrigated catheterassembly can comprise an ablation catheter 15 (e.g., radio frequency(RF), cryoablation, ultrasound, etc.). The instant disclosure generallyrefers to RF ablation electrodes and electrode assemblies, but it iscontemplated that the instant disclosure is equally applicable to anynumber of other ablation electrodes and electrode assemblies where thetemperature of the device and of the targeted tissue areas can befactors during diagnostic and/or therapeutic medical procedures.

Still referring to FIG. 2, the irrigated catheter assembly includes acatheter shaft 17 that is an elongate, tubular, flexible memberconfigured for movement within a body. The catheter shaft 17 can beintroduced into a blood vessel or other structure within a body 19through a conventional introducer. The catheter shaft 17 can be steeredor guided through a body to a desired location such as targeted tissueareas 13 with pullwires, tension elements, so-called push elements, orother means known in the art.

The irrigated catheter assembly further includes at least one fluidlumen or fluid delivery tube 12 disposed within the catheter shaft 17.The fluid delivery tube 12 is configured to supply fluid to the ablationelectrode assembly 10. The fluid delivery tube 12 of the irrigatedcatheter assembly can be connected to a fluid source 21 providing abiocompatible fluid such as saline, or a medicament, through a pump 23,which can comprise, for example, a fixed rate roller pump or variablevolume syringe pump with a gravity feed supply from the fluid source forirrigation. The fluid source 21 and/or pump 23 is conventional in theart. The fluid source 21 and/or pump 23 can comprise a commerciallyavailable unit sold under the name Cool Point™ available from St. JudeMedical, Inc. in an embodiment.

The irrigated catheter assembly can further include one or morepositioning electrodes 51 mounted in or on the catheter shaft 17. Theelectrodes 51 can comprise, for example, ring electrodes. The electrodes51 can be used, for example, with a visualization, navigation, andmapping system 25. The electrodes 51 can be configured to provide asignal indicative of both a position and orientation of at least aportion of the catheter shaft 17. The visualization, navigation, and/ormapping system 25 with which the electrodes 51 can be used can comprisean electric field-based system, such as, for example, that having themodel name ENSITE NAVX (aka EnSite Classic as well as newer versions ofthe EnSite system, denoted as ENSITE VELOCITY) and commerciallyavailable from St. Jude Medical, Inc. and as generally shown withreference to U.S. Pat. No. 7,263,397 titled “Method and Apparatus forCatheter Navigation and Location and Mapping in the Heart,” the entiredisclosure of which is incorporated herein by reference. In accordancewith an electric field-based system, the electrodes 51 can be configuredto be responsive to an electric field transmitted within the body 19 ofthe patient. The electrodes 51 can be used to sense an impedance at aparticular location and transmit a representative signal to an externalcomputer or processor. In other exemplary embodiments, however, thevisualization, navigation, and/or mapping system 25 can comprise othertypes of systems, such as, for example and without limitation: amagnetic field-based system such as the CARTO System (now in a hybridform with impedance- and magnetically-driven electrodes) available fromBiosense Webster, and as generally shown with reference to one or moreof U.S. Pat. No. 6,498,944 entitled “Intrabody Measurement,” U.S. Pat.No. 6,788,967 entitled “Medical Diagnosis, Treatment and ImagingSystems,” and U.S. Pat. No. 6,690,963 entitled “System and Method forDetermining the Location and Orientation of an Invasive MedicalInstrument,” the entire disclosures of which are incorporated herein byreference, or the gMPS system from MediGuide Ltd. of Haifa, Israel (nowowned by St. Jude Medical, Inc.), and as generally shown with referenceto one or more of U.S. Pat. No. 6,233,476 entitled “Medical PositioningSystem,” U.S. Pat. No. 7,197,354 entitled “System for Determining thePosition and Orientation of a Catheter,” and U.S. Pat. No. 7,386,339entitled “Medical Imaging and Navigation System,” the entire disclosuresof which are incorporated herein by reference. In accordance with amagnetic field-based system, the electrodes 51 can be configured to beresponsive to a magnetic field transmitted through the body 19 of thepatient. The electrodes 51 can be used to sense the strength of thefield at a particular location and transmit a representative signal toan external computer or processor. The electrodes 51 can comprise one ormore metallic coils located on or within the catheter shaft 17 in amagnetic field-based system. As noted above, a combination electricfield-based and magnetic field-based system such as the CARTO 3 Systemalso available from Biosense Webster, and as generally shown withreference to U.S. Pat. No. 7,536,218 entitled “Hybrid Magnetic-Based andImpedance-Based Position Sensing,” the entire disclosure of which isincorporated herein by reference, can be used. In accordance with acombination electric field-based and magnetic field-based system, theelectrodes 51 can comprise both one or more impedance-based electrodesand one or more magnetic coils. Commonly available fluoroscopic,computed tomography (CT), and magnetic resonance imaging (MRI)-basedsystems can also be used.

The irrigated catheter assembly can include other conventionalcomponents such as, for example and without limitation, conductorsassociated with the electrodes, and possibly additional electronics usedfor signal processing, visualization, localization, and/or conditioning.The irrigated catheter assembly can further include multiple lumens forreceiving additional components. The irrigated catheter assembly canfurther include a cable connector or interface 27 and a handle 29. Thecable connector or interface 27 can provide mechanical, fluid, andelectrical connection(s) for cables 31, 33, 35 extending from the pump23 and/or an ablation system 37 as described in more detail below. Thecable connector or interface 27 can be conventional in the art and canbe disposed at the proximal end of the irrigated catheter assembly. Thehandle 29 can provide a location for the clinician to hold the irrigatedcatheter assembly and can further provide means for steering or guidingthe catheter shaft 17 within the body 19 as known in the art. Catheterhandles are generally conventional in the art and it will be understoodthat the construction of the handle can vary. In an embodiment, for thepurpose of steering the catheter shaft 17 within the body 19, the handle29 can be substituted by a controllable robotic actuator.

Ablation electrode assembly 10 can be connected to and/or coupled withthe catheter shaft 17. Ablation electrode assembly 10 can be disposed ator near the distal end of the catheter shaft 17. Ablation electrodeassembly 10 can be disposed at the extreme distal end (e.g., tip) of thecatheter shaft 17. Referring now to FIGS. 1 and 3, the ablationelectrode assembly 10 can include an inner core member 14 and an outershell 16 in accordance with a first embodiment of the disclosure. Thelengths and/or diameters of inner core member 14, outer shell 16,ablation electrode assembly 10, as well as portions thereof, can varydepending on the design of ablation electrode assembly 10. The outershell 16 may be about 4 millimeters in length in an embodiment.

Inner core member 14 is provided to interrupt and/or reduce the heattransfer path through the ablation electrode assembly 10 and provide aninsulated internal flow path for irrigation fluid. More particularly,inner core member 14 can be provided to interrupt and/or reduce the heattransfer path between multiple thermal sensors located within theablation electrode assembly 10 as described in more detail below. Byinterrupting and/or reducing the heat transfer path between multiplethermal sensors located within the ablation electrode assembly 10, itcan improve the ability of a catheter incorporating the ablationelectrode assembly 10 to distinguish the higher temperature associatedwith lesion formation at the interface between the electrode of theablation electrode assembly 10 and the targeted tissue.

Inner core member 14 comprises a thermal insulator having a reducedthermal conductivity. Inner core member 14 can be thermallynonconductive in accordance with an embodiment of the disclosure. Innercore member 14 can comprise an electrically nonconductive material inaccordance with an embodiment of the disclosure. In general, the innercore member 14 is lower in thermal conductivity, and preferablysubstantially lower, than outer shell 16. Inner core member 14 cancomprise a reduced thermally conductive polymer in accordance with anembodiment of the disclosure. A reduced thermally conductive polymer isone with physical attributes that decrease heat transfer by about 10% ormore, provided that the remaining structural components are selectedwith the appropriate characteristics and sensitivities desired for theablation electrode assembly 10. One reduced thermally conductivematerial can include polyether ether ketone (PEEK). Additional examplesof thermally nonconductive or reduced thermally conductive materialsthat can be useful in conjunction with the instant disclosure include,but are not limited to, high density polyethylene (HDPE), polyimidethermoplastic resins, such as ULTEM® as provided by General ElectricPlastics (now known as SABIC Innovative Plastics), polyaryletherketones,polyurethane, polypropylene, oriented polypropylene, polyethylene,crystallized polyethylene terephthalate, polyethylene terephthalate,polyester, polyetherimide, acetyl, ceramics, and/or various combinationsthereof. Inner core member 14 can also comprise other plastic materialssuch as silicone or polyether block amides such as those sold under thetrademark PEBAX® and generally available from Arkema France in otherembodiments of the disclosure.

Inner core member 14 has a distal end 18 and a proximal end 20. Innercore member 14 can be generally cylindrical in shape. The distal end 18of the inner core member 14 can be partially spherical or generallyhemispherical in shape in accordance with an embodiment of thedisclosure. The proximal end 20 of the inner core member 14 can beconfigured for coupling and/or connecting inner core member 14 with thecatheter shaft. The proximal end 20 of the inner core member 14 can alsobe configured to receive the fluid delivery tube 12. The inner coremember 14 can include multiple lumens for receiving any number ofcomponents (e.g., wires and the like) which can be routed through theinner core member 14. As best illustrated in FIG. 3, the inner coremember 14 also has an outer surface 22 and an inner surface 24. As bestillustrated in FIG. 4, the outer surface 22 of the inner core member 14includes a channel 26. The outer surface 22 of the inner core member 14includes a plurality of channels 26 in an embodiment of the disclosure.

As best illustrated in FIGS. 1 and 3, each of the plurality of channels26 is configured to receive a thermal sensor 28. Accordingly, theablation electrode assembly 10 can include a plurality of thermalsensors 28 in accordance with an embodiment of the disclosure. Theablation electrode assembly 10 can include three thermal sensors 28 inaccordance with an embodiment of the disclosure. The thermal sensors 28can be substantially equally spaced around the periphery orcircumference of the inner core member 14. Although three sensors thatare substantially equally spaced are mentioned in detail, the ablationelectrode assembly 10 can include fewer or more thermal sensors 28 inother embodiments and the location of the thermal sensors 28 can vary inother embodiments. For example, in an embodiment, a single thermalsensor 28 may be centered within the ablation electrode assembly 10.Thermal sensors 28 can be connected and/or coupled to inner core member14 (and/or ablation electrode assembly 10) in any manner that isconventional in the art to hold thermal sensors 28 in place relative toinner core member 14 (and/or ablation electrode assembly 10). Thermalsensors 28 are configured for measurement and temperaturecontrol/regulation of ablation electrode assembly 10. Thermal sensors 28can be any mechanism known to one of ordinary skill in the art,including for example and without limitation, thermocouples and/orthermistors. Thermal sensors 28 can comprise other types of devices,such as for example and without limitation, devices for determiningpressure, temperature and a flow parameter of a flowing fluid availablefrom Radi Medical Systems AB, and as generally shown with reference toat least U.S. Pat. No. RE39,863 entitled “Combined flow, pressure andtemperature sensor,” the entire disclosure of which is incorporatedherein by reference.

Inner surface 24 defines an inner cavity 30 as best illustrated in FIG.3. In an embodiment of the disclosure, the inner core member 14 includesa radially extending passageway 32 that extends from the inner cavity 30to the outer surface 22 of the inner core member 14. Inner core member14 includes a plurality of radially extending passageways 32 in anembodiment. Each of the radially extending passageways 32 extend fromthe inner cavity 30 of the inner core member 14 to the outer surface 22of the inner core member 14. Each of the radially extending passageways32 can be substantially centrally located on the inner core member 14relative to a longitudinal axis 34 of the ablation electrode assembly10. In an embodiment, the radially extending passageways 32 can beoriented at about 90 degrees relative to the longitudinal axis 34 of theablation electrode assembly 10. In accordance with other embodiments,the radially extending passageways 32 can be angled generally toward thedistal end 18 of the inner core member at an acute angle (e.g., betweenabout 20 to about 70 degrees, and for some embodiments, between about 30to about 65 degrees) with respect to the longitudinal axis 34 of theablation electrode assembly 10. The orientation of the radiallyextending passageways 32 vary depending on the design of the ablationelectrode assembly 10. The radially extending passageways 32 of theinner core member 14 can be straight or curved in various embodiments ofthe disclosure. In accordance with an embodiment of the disclosure, theradially extending passageways 32 of the inner core member 14 can bediametrically opposed to each other around the perimeter orcircumference of the inner core member 14. The radially extendingpassageways 32 can be generally tubular and can have a constant diameteralong their length. In an embodiment, radially extending passageways 32can have a diameter ranging in size from about 0.008 to about 0.015inches, and for some embodiments between about 0.010 to about 0.012inches. Alternate configurations having various shapes and diameters,for example, along all or portions of the length of the radiallyextending passageways 32 can be used in various embodiments. Radiallyextending passageways 32 can be configured to provide proximal deliveryof irrigation fluid. Delivery of irrigation fluid generally reduceschar, thrombus formation, and coagulum formation, thereby enablinggreater energy delivery during RF ablation. Delivery of irrigation fluidcan displace blood and prevent stasis in the areas adjacent the outershell 16 of the ablation electrode assembly 10.

Outer shell 16 improves temperature correlation between the electrodeand tissue interface because it is configured as a thin shell, in placeof a solid mass. The thin shell design can also mitigate temperaturegradients across the ablation electrode assembly 10, as well as mitigatethe effects of orientation of a catheter incorporating the ablationelectrode assembly 10 in connection with monitoring the temperature ofthe ablation electrode assembly 10 and/or targeted tissue.

Outer shell 16 can be a thin shell (i.e., have a small thickness) andcan be external to and/or surround the inner core member 14. Outer shell16 can comprise a single layer. Outer shell 16 can be comprised of anyelectrically, and potentially thermally, conductive material known tothose of ordinary skill in the art for the delivery of ablative energyto targeted tissue areas. Examples of electrically conductive materialsinclude gold, platinum, iridium, palladium, stainless steel, and/or anycombination thereof. In particular, a combination of platinum andiridium can be used in various combinations. Outer shell 16 can befabricated or constructed in accordance with any method or techniqueknown to one of ordinary skill in the art. For example and withoutlimitation, outer shell 16 can be fabricated or constructed usingso-called deep drawn metal forming techniques, metal-punchingtechniques, electroforming techniques (e.g., electroforming over asacrificial form that can include rods or other internal forms that meltor are subsequently dissolved), powdered metal techniques (e.g.,pressing powered metal into a slug, sintering at high heat, and thencovering the pressed and sintered slug with a metallic covering member),liquid metal injection molding (MIM) techniques, and the like. Thepowered metal techniques can also include sacrificial members, and thepressed and sintered slug can itself conduct fluid and thermal energyinside, around, and against the metallic covering.

Outer shell 16 can be electrically connected to an ablation system 37 toallow for the delivery of ablative energy, or the like. Outer shell 16can be electrically connected to an ablation system 37 in any mannerconventional in the art. For example, a power wire 35 (best illustratedin FIG. 7) can be provided within outer shell 16 of ablation electrodeassembly 10. The power wire 35 can extend through a lumen(s) providedwithin the ablation electrode assembly 10. The irrigated catheterassembly can be configured for operation at an initial power setting ofup to 50 Watts.

The ablation system 37 can be comprised of, for example, an ablationgenerator 39 one or more ablation patch electrodes 41. The ablationgenerator 39 generates, delivers, and controls ablation energy (e.g.,RF) output by the irrigated catheter assembly and the outer shell 16 ofthe ablation electrode assembly 10 thereof, in particular. The generator39 is conventional in the art and can comprise a commercially availableunit sold under the model number IBI-1500T RF Cardiac AblationGenerator, available from St. Jude Medical, Inc. In an exemplaryembodiment, the generator 39 can include an RF ablation signal source 43configured to generate an ablation signal that is output across a pairof source connectors: a positive polarity connector SOURCE (+), whichelectrically connects to the outer shell 16 of the ablation electrodeassembly 10 of the irrigated catheter assembly; and a negative polarityconnector SOURCE (−), can be electrically connected to one or more ofthe patch electrodes 41. It should be understood that the termconnectors as used herein does not imply a particular type of physicalinterface mechanism, but is rather broadly contemplated to represent oneor more electrical nodes (including multiplexed and de-multiplexednodes). The source is configured to generate a signal at a predeterminedfrequency in accordance with one or more user specified controlparameters (e.g., power, time, etc.) and under the control of variousfeedback sensing and control circuitry. The source can generate asignal, for example, with a frequency of about 450 kHz or greater for RFenergy. The generator 39 can also monitor various parameters associatedwith the ablation procedure including, for example, impedance, thetemperature at the distal tip of the irrigated catheter assembly,applied ablation energy, power, force, proximity, and the position ofthe irrigated catheter assembly, and provide feedback to the clinicianor another component within the irrigated catheter assembly regardingthese parameters. Operation in a temperature control mode can be, forexample, at a set point above 50 degrees Celsius.

Outer shell 16 has a distal end 36 and a proximal end 38. Outer shell 16can be generally cylindrical in shape. The distal end 36 of the outershell 16 can be partially spherical or generally hemispherical in shapein accordance with an embodiment of the disclosure. The proximal end 38of outer shell 16 can be configured for connection to the inner coremember 14. Outer shell 16 can be coupled together or connected withinner core member 14 along the same longitudinal axis 34. Inner coremember 14 and outer shell 16 can be connected or coupled together by anyknown mechanisms including, for example and without limitation, adhesivebonding, press-fit configurations, snap-fit configurations, ultrasonicstaking, mechanical deformation, or any other mechanism known to one ofordinary skill in the art. In an embodiment, a connecting member 40 canbe used to connect the outer shell 16 to the inner core member 14. Forexample, the connecting member 40 can comprise a generally annular ring42 and a radially outwardly extending flange 44 at an axial (e.g.,proximal) end of the generally annular ring 42. The generally annularring 42 can have an outer diameter that is substantially equal to theinner diameter of the outer shell 16 at the proximal end 38 of the outershell 16. The radially outwardly extending flange 44 of the connectingmember 40 can have an outer diameter that is substantially equal to theouter diameter of the outer shell 16. At least a portion of the outershell and the radially outwardly extending flange 44 can be connectedusing any of the mechanisms for connection described above. In theembodiment described above, the connecting member 40 can be separatefrom the remainder of the inner core member 14, such that the inner coremember 14 and connecting member 40 form a multiple-piece assembly. Inother embodiments, the connecting member 40 can be integral with theinner core member 14, such that the inner core member 14 and connectingmember 40 form a single-piece assembly.

The outer shell 16 also has an outer surface 46 and inner surface 48 asbest illustrated in FIG. 3. As best illustrated in FIG. 4, the outersurface 46 of the outer shell 16 can be scored with at least one slot50. The outer surface 46 of the outer shell 16 can be scored with aplurality of grooves or slots 50 in accordance with an embodiment of thedisclosure. Each of the plurality of grooves or slots 50 can extendaxially, parallel to the longitudinal axis 34 of the ablation electrodeassembly 10. Each of the plurality of grooves or slots 50 can extendfrom the proximal end 38 of the outer shell 16 toward the distal end 36of the outer shell 16. Each of the plurality of grooves or slots 50 canextend for a substantial portion of the axial length of the outer shell16. Each of the plurality of grooves or slots 50 can be configured toseparate the outer shell 16 into a plurality of segments. The ablationelectrode assembly 10 can include a separate, individual thermal sensor28 for each of the plurality of segments of the outer shell 16. Byseparating the outer shell 16 into a plurality of segments, morecomplete segregation of individual thermal sensors 28 can be obtained.In an embodiment, at least one retaining wire and/or safety wire (notshown) can be extended through a lumen in the catheter shaft and can beconnected to the ablation electrode assembly 10. The retaining wireand/or safety wire can be configured to ensure that that the ablationelectrode assembly 10 is not separated from the catheter shaft to whichit is attached during movement of the irrigated catheter assembly withina body.

Inner core member 14 and outer shell 16 define a space 52. Space 52 canfurther interrupt and/or reduce the heat transfer path between multiplethermal sensors 28. The configuration of the space 52 can vary greatlyand can be regular or irregular and can include support members (e.g.,flutes, bosses, posts, and the like) to maintain separation and auseable space between the shells. The space 52 can be configured as anannular space in accordance with an embodiment of the invention. Inaccordance with an embodiment of the disclosure, the space 52 cancomprise a vacuum region or evacuated region. The vacuum space orevacuated region serves as an insulator, thereby reducing convectionheat transfer phenomena.

In accordance with an embodiment of the disclosure, the ablationelectrode assembly 10 further includes an irrigant distribution element54. Irrigant distribution element 54 can be configured as a generallyannular ring in accordance with an embodiment of the disclosure. Theirrigation distribution element 54 has a proximal end 56 and a distalend 58. At least a portion of the proximal end 56 of the irrigantdistribution element 54 can engage a catheter shaft in which the innercore member 14 can be located. At least a portion of the distal end 58of the irrigant distribution element 54 can surround and/or encircle theinner core member 14 and, further, can define a circumferentialirrigation port 60 between the irrigant distribution element 54 and theinner core member 14 in accordance with an embodiment of the disclosure.Irrigant distribution element 54 is configured to guide irrigation fluidtoward outer shell 16 about and along outer surface 46 of the outershell 16, and in particular, direct the fluid (e.g., irrigant) flow in adirection substantially parallel with the outer surface 46 of the outershell 16. Irrigant distribution element 54 can include a fluid shapingmember 61 that helps ensure that the fluid flow tends toward the surface46 of the outer shell 16 of the ablation electrode assembly 10. Forexample and without limitation, the fluid shaping member 61 of theirrigant distribution element 54 can include a channel, rifling, boss,hump, chamfer, and/or combination thereof on a surface defining thecircumferential irrigation port 60. The fluid shaping member 61 isconfigured to disturb fluid flow (e.g., cause fluid flowing closer tothe outer surface of the inner core member 14 to slow down relative tofluid flowing farther from the outer surface of the inner core member14), thereby helping to ensure that the fluid flow tends toward thesurface 46 of the outer shell 16.

Referring now to FIGS. 5 and 6, the ablation electrode assembly 110 caninclude an inner core member 114 and an outer shell 116 in accordancewith a second embodiment of the disclosure. The inner core member 114and outer shell 116 of the ablation electrode assembly 110 in accordancewith a second embodiment of the disclosure can be substantiallyidentical to the inner core member 14 and outer shell 16 of the ablationelectrode assembly 10 as described herein, except that the inner coremember 114 and outer shell 116 can be modified to provide both proximaland distal delivery of irrigation fluid. The ablation electrode assembly110 is configured to provide both proximal and distal delivery ofirrigation fluid, can be especially beneficial to reduce thrombusformation and/or charring at the distal end (e.g., tip) of the ablationelectrode assembly 110. By providing both proximal and distal deliveryof irrigation fluid, it can further displace blood and prevent stasis inthe areas adjacent the outer shell 116 of the ablation electrodeassembly 110.

Ablation electrode assembly 110 is configured for distal delivery ofirrigation fluid with an axially extending passageway 162 extending fromthe inner cavity 130 of the inner core member 114 to the distal end 118of the inner core member 114. The inner core member 114 can furtherinclude a distal end portion 164 and the outer shell 116 can include anaperture 166 at distal end 136 of the outer shell 116. The distal endportion 164, coupled with aperture 166, can enable irrigation fluidflowing through the axially extending passageways 162 to flow to adistal end 136 (e.g., tip) of outer shell 116, therein substantiallyirrigating the distal end 136 (e.g., tip) of outer shell 116 of theablation electrode assembly 110. Outer shell 16, 116 does not includeany radially extending aperture in accordance with an embodiment of thedisclosure. Distal end portion 164 can extend distally from thepartially spherical and/or generally hemispherical distal end 118 of theinner core member 114 and can be generally cylindrical in shape. Distalend portion 164 can extend within the aperture 166 at distal end 136 ofthe outer shell 116. Distal end portion 164 can include one or moreports 168 extending from the axially extending passageway 162. Forexample and without limitation, distal end portion 164 can include threeports. Each of the ports 168 can be oriented at an acute angle (e.g.,about 45 degrees) relative to the longitudinal axis 134 of the ablationelectrode assembly 110. The orientation of the ports 168 variesdepending on the design of the ablation electrode assembly 110. Theports 168 may be substantially equally spaced around the circumferenceof the distal end portion 164 in an embodiment. The axially extendingpassageway 162 extends through the distal end portion 164. Distal endportion 164 can comprise the same material as the inner core member 114.In other embodiments, the axially extending passageway 162 can extenddirectly through the distal end 36 of the outer shell 116.

In an embodiment of the disclosure, a coating (not shown) can bedisposed on at least a portion of the inner core member 114 and/or outercore member 116 that defines the axially extending passageway 162. Thecoating can be comprised of an electrically nonconductive material. Thecoating can be comprised of diamond, diamond-like carbon (DLC) orpolytetrafluoroethylene (PTFE), which is commonly sold by the E. I. duPont de Nemours and Company under the trade name Teflon®. In anembodiment, the coating can be provided around the entire circumferenceand along the entire length of the axially extending passageway 162.However, the coating can be provided only around a portion of thecircumference and/or only around a portion of the length of the axiallyextending passageway 162 in accordance with various embodiments of thedisclosure. The amount of the coating provided around the circumferenceand/or length of the axially extending passageway 162 or portion thereofcan vary depending on the relative requirements of ablation electrodeassembly 110.

Referring now to FIGS. 7 and 8, the ablation electrode assembly 210 caninclude an inner core member 214 and an outer shell 216 in accordancewith a third embodiment of the disclosure. The inner core member 214 andouter shell 216 of the ablation electrode assembly 210 in accordancewith a third embodiment of the disclosure can be substantially identicalto the inner core member 14 and outer shell 16 of the ablation electrodeassembly 10 in accordance with a first embodiment of the disclosure asdescribed herein, except that the inner core member 214 and outer shell216 can be modified to allow for the flow of irrigation fluid in theannular space 252 between the inner core member 214 and outer shell 216.

Ablation electrode assembly 210 is configured for allowing the flow ofirrigation fluid in the annular space 252 between the inner core member214 and the outer shell 216 by including an aperture 268 located at thedistal end 218 of the inner core member 214. The inner core member 214also includes an axially extending passageway 262. The fluid deliverytube 12 can be in fluid communication with the axially extendingpassageway 262. The axially extending passageway 262 can terminate ataperture 268 located at the distal end 218 of the inner core member.Irrigation fluid from the axially extending passageway 262 can flow outof the aperture 268 in a first direction toward the distal end 236 ofthe outer shell 216. The irrigation fluid can then flow radiallyoutwardly from the aperture 268 and can then eventually flow back in asecond direction (i.e., opposite the first direction) toward theproximal end 238 of the outer shell 216 in the annular space 252 betweenthe outer shell 216 and the inner core member 214. Irrigation fluidflowing in the annular space 252 can absorb heat from both thecirculating blood pool and the lesion being created in the targetedtissue during RF ablation. The irrigation fluid can then exit theannular space 252 between the outer shell 216 and the inner core member214 and can flow through a collection channel 254 and then flow througha first radially extending passageway 232 of the inner core member 214.The first radially extending passageway 232 of the inner core member 214can be similar to radially extending passageway 32 of inner core member14, 114, except that the first radially extending passageway 232 cannotextend from the inner cavity 30 to the outer surface 22 of the innercore member 214. The first radially extending passageway 232 of theinner core member 214 instead extends from the collection channel 254(and thus, the annular space 252), thereby allowing irrigation fluidthat has flowed through the annular space 252 to exit the ablationelectrode assembly 210. Delivery of irrigation fluid generally reduceschar, thrombus formation, and coagulum formation, thereby enablinggreater energy delivery during RF ablation. Delivery of irrigation fluidcan also displace blood and prevent stasis in the areas adjacent theouter shell 216 of the ablation electrode assembly 210.

Accordingly, the annular space 252 is in fluid communication with boththe inner cavity 230 of the inner core member 214 (e.g., through theaxially extending passageway 262), as well as the first radiallyextending passageway 232. In an embodiment where the ablation electrodeassembly 210 further includes irrigant distribution element 54, thedistal end 58 of irrigant distribution element 54 can define acircumferential irrigation port 60 between the irrigant distributionelement 54 and the inner core member 214. Irrigation fluid exiting thefirst radially extending passageway 232 can flow out the circumferentialirrigation port 60 as best illustrated in FIG. 8.

FIG. 9 is a flow diagram generally representing an exemplary method ofusing an ablation electrode assembly 210 (or 310 as describedhereinbelow) to provide irrigation fluid and/or control temperatureduring cardiac ablation of targeted tissue. In an embodiment ofproviding irrigation fluid during cardiac ablation of targeted tissue, acatheter is used in Step 400. The catheter can comprise a catheter shafthaving a fluid lumen or fluid delivery tube 12 and an electrode assembly210, 310 connected to the catheter shaft. The electrode assembly 210,310 can include an inner core member 214, 314 having a distal end 218,318 and a proximal end 220, 320. The inner core member 214, 314 caninclude an outer surface 222, 322 and an inner surface 224, 324. Theinner surface can define an inner cavity 230, 330. The inner core member214, 314 can further include a first radially extending passageway 232,332 that extends through the outer surface 222 of the inner core member214. The inner core member 214, 314 can further include an axiallyextending passageway 262, 362 extending from the inner cavity 230, 330to the distal end 218, 318 of the inner core member 214, 314. Theelectrode assembly 210, 310 can further include an outer shell 216, 316surrounding the inner core member 214, 314. The outer shell 216, 316 canhave a distal end 236, 336 and a proximal end 238, 338. The ablationelectrode assembly 210, 310 can further include plurality of thermalsensors 28. In an embodiment, the outer shell 216 can be scored with aplurality of axially extending grooves or slots 50 to separate the outershell 216, 316 into a plurality of circumferentially-extending segments.In this embodiment, there can be a thermal sensor 28 for each of theplurality of segments of the outer shell 216, 316. Accordingly, each ofthe plurality of segments of the outer shell 216, 316 can have at leastone corresponding thermal sensor 28 out of the plurality of thermalsensors 28. The inner core member 214, 314 and the outer shell 216, 316can define an annular space 252, 352. Energy is delivered to the outershell 216, 316 of the electrode assembly 210, 310 in Step 402. Inparticular, the outer shell 216, 316 of the electrode assembly 210, 310is electrically connected to an ablation system 37 including an ablationgenerator 39 for generating and delivering energy to the catheter. Theenergy generated and delivered to the catheter 15 from the ablationgenerator 39 can be based at least in part on the highest temperaturemeasurement from the plurality of thermal sensors 28 utilized inconnection with the ablation electrode assembly 210, 310, both inembodiments where the outer shell 216, 316 is not separated into aplurality of segments and in embodiments where the outer shell 216, 316is separated into a plurality of segments.

Irrigation fluid is directed from the fluid lumen or fluid delivery tube12 to the inner cavity 30 of the inner core member 214, 314 in Step 404.At least a first portion of the irrigation fluid is allowed to flow fromthe inner cavity 30 of the inner core member 214, through the axiallyextending passageway 262 in the inner core member 214, and into theannular space 252 between the inner core member 214 and the outer shell216 in Step 406. In accordance with one embodiment of the disclosure asgenerally illustrated in FIGS. 7 and 8, all of the irrigation fluid fromthe inner cavity 230 of the inner core member 214 (and thus all of theirrigation fluid delivered by the fluid delivery tube 12) can bedirected from the inner cavity 230, through the axially extendingpassageway 262, and into the annular space 252. In accordance with otherembodiments of the disclosure as generally illustrated in FIGS. 10 and11, only a portion (i.e., a first portion) of the irrigation fluid fromthe inner cavity 30 of the inner core member 314 (and thus only aportion of the irrigation fluid delivered by the fluid delivery tube 12)can be directed from the inner cavity 330, through the axially extendingpassageway 362, and into the annular space 352.

At least the first portion of the irrigation fluid from the inner cavity230, 330 of the inner core member 214, 314 is directed away from theannular space 252, 352 between the inner core member 214, 314 and theouter shell 216, 316 in Step 408. As described above, in someembodiments all of the irrigation fluid from the inner cavity 230, 330of the inner core member 214 can be directed into the annular space 252,352, and so all of the irrigation fluid from the inner cavity 230, 330of the inner core member 214, 314 can be directed from the annular space252 in Step 408. In other embodiments, only a portion (i.e., a firstportion) of the irrigation fluid from the inner cavity 230, 330 of theinner core member 214, 314 (and thus only a portion of the irrigationfluid delivered by the fluid delivery tube 12) can be directed away fromthe annular space 252, 352. In some embodiments, the first portion ofthe irrigation fluid is directed away from the annular space 252, 352 tothe first radially extending passageway 232, 332. In other embodiments,the first portion of the irrigation fluid is directed away from theannular space 252, 352 toward a proximal end of the catheter forelimination from the catheter at a location that is remote from apatient.

In the embodiments where only a portion (i.e., a first portion) of theirrigation fluid from the inner cavity 230, 330 of the inner core member214, 314 is directed to the annular space 252, 352 and to the firstradially extending passageway 232, 332 or toward the proximal end of thecatheter for elimination from the catheter at a location that is remotefrom a patient, the inner core member 214, 314 includes a secondradially extending passageway 333 as illustrated in FIGS. 10 and 11. Thesecond radially extending passageway 333 extends from and is in directfluid communication with the inner cavity 330 to the outer surface 322of the inner core member 314. The second radially extending passageway333 of the inner core member 314 can be similar to radially extendingpassageway 32, 132 of inner core member 14, 114. In accordance with thisembodiment of the disclosure as generally illustrated in FIGS. 10 and11, fluid that has flowed through the axially extending passageway 362and/or the annular space 352 does not flow through the second radiallyextending passageway 333 and instead flows through the first radiallyextending passageway 332 as described hereinabove. At least anotherportion (i.e., a second portion) of the irrigation fluid from the innercavity 330 of the inner core member 314 can be directed directly to thesecond radially extending passageway 333, thereby allowing for proximaldelivery of irrigation fluid. Delivery of irrigation fluid generallyreduces char, thrombus formation, and coagulum formation, therebyenabling greater energy delivery during RF ablation. Delivery ofirrigation fluid can also displace blood and prevent stasis in the areasadjacent the outer shell 316 of the ablation electrode assembly 310. Thefirst portion of the irrigation fluid (i.e., the portion of irrigationfluid that is directed to the annular space 352 and to the collectionchannel 354 and to the first radially extending passageway 332) can beseparate from the second portion of the irrigation fluid (i.e., theportion of irrigation fluid that is directed to the second radiallyextending passageway 333).

The irrigation fluid flowing in the annular space 252, 352 can absorbheat from the circulating blood pool and the lesion being developed atthe targeted tissue during RF ablation in which energy is delivered tothe outer shell 216, 316 of the electrode assembly 210, 310. Bymonitoring the change in temperature of the irrigation fluid as it flowsthrough the annular space 252, 352, it can be possible to estimate theenergy removed from the ablation electrode assembly 210, 310 during anablation cycle, thereby making it possible to better estimate the energyactually delivered to the targeted tissue.

In accordance with the embodiment of the ablation electrode assembly 310generally illustrated in FIGS. 10 and 11, the flow rate of the secondportion of the irrigation fluid (i.e., the portion of irrigation fluidthat is directed to the second radially extending passageway 333) can begreater than the flow rate of the first portion of the irrigation fluid(i.e., the portion of irrigation fluid that is directed to the annularspace 352 and to the collection channel 354 and to the first radiallyextending passageway 332). For example and without limitation, the flowrate of irrigation fluid from the fluid delivery tube 12 can beapproximately 6-10 ml/minute, and the flow rate of the first portion ofthe irrigation fluid can be only approximately 1-3 ml/minute. Inparticular, aperture 368 can be configured to allow a flow rate forirrigation fluid of approximately 1-3 ml/minute. Accordingly, themajority of the irrigation fluid delivered by the fluid delivery tube 12can be directed out of the second radially extending passageway 333. Theflow rate of the second portion of the irrigation fluid can beapproximately 3-9 ml/minute. Although these flow rates are mentioned indetail, the various flow rates can be greater or smaller in accordancewith other embodiments of the disclosure. In this way, only a relativelysmall amount of irrigation fluid from the fluid delivery tube 12 isdirected through the outer shell 316 of the ablation electrode assembly310, while the majority of the irrigation fluid from the fluid deliverytube 12 is ejected out of the irrigant distribution element 54.Accordingly, ablation electrode assembly 310 allows for the additionalsteps of measuring temperatures of at least a first portion of theirrigation fluid as described in more detail below, while providing ahigher secondary flow rate of irrigation fluid that is sufficient toflush the surface of the ablation electrode assembly 310 and displaceblood at the lesion site in the targeted tissue. Irrigation fluiddirected to the second radially extending passageway 333 with theirrigant distribution element 54 can help reduce charring and inhibitthe formation of coagulum and/or soft thrombus by mixing, displacingand/or diluting blood that can be in contact with ablation electrodeassembly 310.

In some embodiments, the overall total fluid volumes associated with theflow rate of the first portion of the irrigation fluid combined with theflow rate of the second portion of the irrigation fluid can be muchlower than prior art or typically utilized in clinical practice. Thatis, overall total fluid volume can range from low single digits to lessthan about two or so milliliters per minute while effectively reducingor eliminating char and coagulum and improving temperature correlationfor more precise control of temperature during ablation procedures. Inan embodiment, overall total fluid volume delivered to a patient can bewell below about seven or so milliliters per minute or less. Such lowoverall total fluid volumes can be especially valuable for patientsalready suffering from fluid overload (e.g., patient having heartfailure and the like). Of course, for patients that can tolerate fluidintake or for procedures seeming to require higher fluid delivery ratesor volumes, the embodiments herein can accommodate same.

A first temperature T_(in) of at least the first portion of theirrigation fluid is measured at a first location L_(in) near where atleast the first portion of the irrigation fluid enters the inner cavity230, 330 of the inner core member 214, 314 and/or where at least thefirst portion of the irrigation fluid enters the axially extendingpassageway 262, 362 from the inner cavity 230, 330 in Step 410. A firstthermal sensor 28 is used to measure the first temperature T_(in). Asecond temperature T_(out) of at least the first portion of theirrigation fluid is measured at a second location L_(out) near where atleast the first portion of the irrigation fluid exits the electrodeassembly 210, 310 in Step 412. In one embodiment, the second locationcan be near where at least the first portion of the irrigation fluidexits the radially extending passageway 232, 332. In other embodiments,the second location can be near where at least the first portion of theirrigation fluid exits the electrode assembly 210, 310 for eventualelimination from the catheter at a location remote from a patient. Asecond thermal sensor 28 is used to measure the second temperatureT_(out).

A temperature differential value ΔT is calculated based at least in parton the first temperature T_(in) and the second temperature T_(out) inStep 414. An electronic control unit (ECU) 45 can be in connection withthe thermal sensors 28 and can be used to calculate the temperaturedifferential value. A display device 47 can also be used in connectionwith the ablation electrode assembly 210, 310 and ECU 45. The ECU 45preferably comprises a programmable microprocessor or microcontroller,but can alternatively comprise an application specific integratedcircuit (ASIC). The ECU 45 can include a central processing unit (CPU)and an input/output (I/O) interface through which the ECU 45 can receiveinput data (e.g., temperature measurements from thermal sensors 28) andcan generate output data (e.g., temperature differential value ΔT). Thetemperature differential value δT is calculated in accordance with thefollowing equation:ΔT=(T _(out) −T _(in))  (Equation 1)

A first value Q₁ indicative of energy delivered to at least the firstportion of the irrigation fluid as it flows from the first location(i.e., where the irrigation fluid enters the inner cavity 230, 330 ofthe inner core member 214, 314 and/or where the irrigation fluid entersthe axially extending passageway 262, 326 from the inner cavity 230,330) to the second location (i.e., where the irrigation fluid exits theradially extending passageway 232, 332) is calculated based at least inpart on the temperature differential value ΔT in Step 416. The ECU 45can be used to calculate the first value Q₁. The first value Q₁ iscalculated in accordance with the following equation, where m=mass ofthe irrigation fluid and Cp=specific heat of the irrigation fluid.Q ₁ =mCp(T _(out) −T _(in))  (Equation 2)

The catheter 15 to which the ablation electrode assembly 210, 310 can beconnected can include a memory such as an EEPROM that stores numericalvalues for the coefficient (e.g., specific heat of the irrigation fluidreferred to as Cp in Equation 2) or stores a memory address foraccessing the numerical values in another memory location (either in thecatheter EEPROM or in another memory). The ECU 45 can also have amemory. The ECU 45 can retrieve these values or addresses directly orindirectly from the memory of the catheter 15 or the ECU 45. The inputdata and output data acquired and generated by the ECU 45 can also bestored in the memory of the catheter 15 or the ECU 45. As describedabove, the input data can include the first and second temperaturesT_(in) and T_(out) obtained by the thermal sensors 28. The input datacan further include information regarding the flow rate of irrigationfluid obtained from a control system 49 and described in more detailbelow. The flow rate can be used to obtain information regarding themass of the irrigation fluid referred to as m in Equation 2. Asdescribed above, the output data can include the temperaturedifferential value ΔT and/or the first value Q₁.

A second value Q₂ indicative of energy delivered to the targeted tissueis calculated based at least in part on the first value Q₁ in Step 418.The ECU 45 can be used to calculate the second value Q₂. The secondvalue Q₂ is calculated in accordance with the following equation, whereE=electrical energy provided to the ablation electrode assembly 210, 310(E=P×t, where P=power and t=time):Q ₂ =E−Q ₁  (Equation 3)

The output data can further include the second value Q₂. The delivery ofenergy to ablation electrode assembly 210, 310 is preferably controlledby the control system 49. The control system 49 is configured todetermine the temperature of the tissue to be ablated and/or anappropriate ablation technique. The outer shell 216, 316 of the ablationelectrode assembly 210, 310 is connected to the control system 49 withwires. The ablation generator 39 can form part of the control system 49or can be separate from the control system 49 in other embodiments.Thermal sensors 28 are also connected to the control system. For exampleand without limitation, wires can extend through lumens in the catheter.Devices for determining pressure, temperature, and a flow parameter of aflowing fluid available from Radi Medical Systems AB, and as generallyshown with reference to at least U.S. Pat. No. RE39,863 entitled“Combined flow, pressure and temperature sensor,” the entire disclosureof which is incorporated herein by reference can be used to monitorand/or control the quantity of flow of irrigation fluid within or fromthe catheter at one or more locations using a flow-from pressurealgorithm. These devices for determining pressure, temperature, and aflow parameter of a flowing fluid are also connected to the controlsystem. The ECU 45 and display device 47 can also be connected to thecontrol system 49.

The control system 49 can be configured to adjust the amount of energy Egenerated and delivered to the catheter 15 from the ablation generator39 based at least in part on the temperature differential value ΔT inaccordance with an embodiment of the disclosure. For example, a greatertemperature differential value ΔT suggests that more energy is beingremoved from the ablation electrode assembly 210, 310, such that theablation generator 39 can be configured to provide more energy to theablation electrode assembly 210, 310. The energy provided to theablation electrode assembly 210, 310 can be increased by increasing thepower and/or the length of time of energy delivery (e.g., frequencyand/or operating time) during the ablation cycle. For example, a lowertemperature differential value ΔT suggests that less energy is beingremoved from the ablation electrode assembly 210, 310, such that theablation generator 39 can be configured to provide less energy to theablation electrode assembly 210, 310. The energy provided to theablation electrode assembly 210, 310 can be decreased by decreasing thepower and/or length of time of energy delivery (e.g., frequency and/oroperating time) during the ablation cycle.

The temperature differential value ΔT for the irrigation fluid can becorrelated to the actual temperature of the targeted tissue during RFablation, and data regarding the correlation between the temperaturedifferential value ΔT and the actual temperature of the targeted tissuecan be stored by the ECU 45 or memory of catheter 15. The correlationbetween the temperature differential value ΔT and the actual temperatureof the targeted tissue can be determined by utilization of the thermalproperties and flow rates of the irrigation fluid to obtain informationregarding the energy state of the external environment (i.e., thetargeted tissue). In this way, the control system 49 can be configuredto use the temperature differential value ΔT for the irrigation fluid inorder to estimate the temperature of the targeted tissue 13 (or theinterface between the ablation electrode assembly 210, 310 and thetargeted tissue 13) and ultimately select an appropriate ablationtechnique. The ablation technique that is selected can be selected toproduce a certain, predetermined temperature in the targeted tissue 13that will form a desired lesion in the targeted tissue. While thedesired lesion can be transmural in some embodiments, thecharacteristics of the desired lesion can vary significantly. Thecertain, predetermined temperature in the targeted tissue 13 that willform a desired lesion in the targeted tissue 13 can be affected by thethermal response of the targeted tissue. The thermal response of thetargeted tissue 13 can be affected by a number of variables includingtissue thickness, amount of fat and muscle, blood flow through theregion, and blood flow at the interface of the ablation electrodeassembly 210, 310 and the targeted tissue 13.

FIG. 12 is an exemplary chart comparing the temperature of the distalend (i.e., tip) of ablation electrode assemblies with the temperature ofthe targeted tissue over time. As generally illustrated in FIG. 12, thetemperature recorded at the distal end (i.e., tip) of ablation electrodeassemblies typically lags that of the targeted tissue. Moreover, thetemperature recorded at the distal end (i.e., tip) of ablation electrodeassemblies plateaus, resulting in an even more significant differencefrom the temperature of the targeted tissue. Difference between thetemperature recorded at the distal end (i.e., tip) of ablation electrodeassemblies and targeted tissue is most acute in connection with ablationelectrode assemblies that are un-insulated. Although ablation electrodeassemblies having an insulated tip (including ablation electrodeassemblies 10, 110, 210, 310) have an improved correlation between thetemperatures of the distal end (i.e., tip) of the ablation electrodeassemblies 10, 110, 210, 310 with the temperatures of the targetedtissues as generally illustrated in FIG. 12, RF ablation would benefitfrom an even more improved correlation between the temperatures ofablation electrode assemblies and targeted tissues.

FIG. 13 is a flow diagram generally representing an exemplary method ofusing an ablation electrode assembly 10, 110, 210, 310 to provideirrigation fluid during cardiac ablation of targeted tissue in an effortto further improve the correlation between the temperatures of thedistal ends (i.e., tips) of ablation electrode assemblies 10, 110, 210,310 and the targeted tissues. In particular, a pulsatile flow ofirrigation fluid can be utilized to increase flow turbulence and helpprevent stagnation areas. Although pulsatile flow is mentioned in detailin accordance with some embodiments of the invention, ablation electrodeassemblies 10, 110, 210, 310 can be used in connection with any type offlow of irrigation fluid. For example and without limitation, pulsatileflow, intermittent flow, constant flow, and/or variable flow ofirrigation fluid can be used in connection with ablation electrodeassemblies 10, 110, 210, 310.

In an embodiment of providing irrigation fluid during cardiac ablationof targeted tissue, a catheter is used in Step 500. The catheter 15 cancomprise a catheter shaft 17 having a fluid lumen or fluid delivery tube12 and an electrode assembly 10, 110, 210, 310 connected to the cathetershaft. The electrode assembly 10, 110, 210, 310 can include an innercore member 14, 114, 214, 314 and an outer shell 16, 116, 216, 316. Theinner core member 14, 114, 214, 314 and the outer shell 16, 116, 216,316 can define an annular space 52, 152, 252, 352 therebetween. Inaccordance with an embodiment of the invention, a pulsatile flow ofirrigation fluid can be directed within at least a portion of at leastone of the inner core member 14, 114, 214, 314 and outer shell 16, 116,216, 316 in Step 502. The irrigation fluid has a first flow rate in afirst time period and has a second flow rate in a second time period.The first flow rate and the second flow rate can alternate and recur atintervals over time. The first flow rate and the second flow rate canalternate and recur at regular intervals in accordance with someembodiments of the disclosure and/or can alternate and recur atirregular intervals in accordance with other embodiments of thedisclosure. The first flow rate and the second flow rate can beintermittent in an embodiment of the disclosure. In accordance with anembodiment of the disclosure, the second flow rate is greater than thefirst flow rate. For example and without limitation, the first flow ratecan be approximately 2 ml/min, and the second flow rate can beapproximately 13 ml/min. In accordance with other embodiments of thedisclosure, the first flow rate can be greater than the second flowrate. Accordingly, the irrigation fluid is a pulsatile flow inalternating waves of low flow rates and high flow rates, where either alow flow rate occurs first or a high flow rate occurs first. Utilizationof a first flow rate of irrigation fluid that is higher and a secondflow rate of irrigation fluid that is lower can be preferred in somestepped irrigation sequences. Although these particular flow rates arementioned in detail, the first and second flow rates can be smaller orgreater in other embodiments of the disclosure.

The use of a pulsatile flow rate allows the temperature measurement fromthe thermal sensors 28 at the outer shell 16, 116, 216, 316 of theablation electrode assembly 10, 110, 210, 310 as described herein toincrease temporarily during the time period with a lower flow rate(i.e., the first time period), thereby bringing the temperaturemeasurement from the thermal sensors 28 closer to the actual temperatureof the interface between the ablation electrode assembly 10, 110, 210,310 and the targeted tissue 13 so that the thermal sensors 28 moreclosely reflect the actual temperature. In particular, the method ofusing an ablation electrode assembly 10, 110, 210, 310 to controltemperature during cardiac ablation of targeted tissue 13 can utilize anextended period of low flow (i.e., the first flow rate) early in thepower delivery ablation cycle in order to provide a so-called “warm-up”sequence. The use of a pulsatile flow with an ablation electrodeassembly 10, 110, 210, 310 having an inner core member 14, 114, 214, 314and an outer shell 16, 116, 216, 316 can benefit most from the wave(s)of lower flow rates because the ablation electrode assembly 10, 110,210, 310 already has an improved correlation between the temperatures ofthe ablation electrode assemblies 10, 110, 210, 310 and the targetedtissue. During the time period with a higher flow rate (i.e., the secondtime period), the ablation electrode assembly 10, 110, 210, 310 bestreceives the benefits of tissue cooling and coagulum reduction.Accordingly, the method of using an ablation electrode assembly 10, 110,210, 310 to control temperature during cardiac ablation of targetedtissue can utilize higher flow rates (i.e., the second flow rate) toreduce the temperature of the interface between the electrode ablationassembly 10, 110, 210, 310 and the targeted tissue. In an exemplaryembodiment of the disclosure, the method of using an ablation electrodeassembly 10, 110, 210, 310 to control temperature during cardiacablation of targeted tissue can employ the following pattern of flowrates: (1) an initial warm-up period; (2) a first flow rate (e.g., 2ml/min) for a first time period (e.g., 6 seconds); (3) a first cool-downperiod; (4) a second flow rate (e.g., 13 ml/min) for a second timeperiod (e.g., 4 seconds); (5) a recovery period; (6) a first flow rate(e.g., 2 ml/min) for a first time period (e.g., 6 seconds); (6) a secondcool-down period; and (7) a second flow rate (e.g., 13 ml/min) for asecond time period (e.g., 4 seconds). Pulsatile flow of irrigation fluidcan also help prevent stagnation areas and increase flow turbulence,which can help prevent stasis and the formation of coagulum.

Valve members, for example and without limitation, such as those shownand described in co-owned U.S. Patent Application Publication No.2008/0161795, or other similar flow control features can be used inconnection with catheters incorporating ablation electrode assemblies10, 110, 210, 310 in order to alternate between first and second flowrates. In other embodiments, the flow control features can be part of anancillary control system separate from and to be used in conjunctionwith catheters. The valves can operate automatically without user inputand/or can operate based on feedback recorded during RF ablation by theECU 45. The feedback can relate to time, temperature, and/or impedance,for example and without limitation. For example, the first and secondflow rates can be based at least in part on temperature measurementstaken by the thermal sensors 28. For example, as temperaturemeasurements from thermal sensors 28 increase, a higher flow rate can bedesirable. For another example, as temperature measurements from thermalsensors 28 decrease, a lower flow rate can be desirable. The thermalsensors 28 can thus provide feedback which can be implemented in acontrol algorithm executed by the ECU 45 and/or control system 49 toautomatically control the flow rates of irrigation fluid withincatheters incorporating ablation electrode assembly 10, 110, 210, 310.For example, the first and second flow rates can be based at least inpart on an impedance measurement taken by a positioning electrode asdescribed hereinabove. In particular, the positioning electrodes can beused to sense an impedance at a particular location and transmit arepresentative signal to an external computer or processor (i.e., theECU 45). Circuitry for implementing the feedback automatically in acontrol algorithm can be readily provided by those having ordinary skillin the art after becoming familiar with the teachings herein. Althoughpulsatile flow of irrigation fluid is mentioned and described in detail,other flow patterns for irrigation fluid (e.g., intermittent, constant,variable) can be used in connection with other embodiments of theinvention.

Although at least four embodiments of this disclosure and at least twomethods of use therefor have been described above with a certain degreeof particularity, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thespirit or scope of this disclosure. For example, additional thermalsensors can be connected to the ablation electrode assemblies (e.g.,external to the outer shell) for additional temperature measurements.For another example, although the ablation electrode assemblies includean irrigation port as described and illustrated and although exemplarymethods of using ablation electrode assemblies to provide irrigationfluid have been described and illustrated, the ablation electrodeassemblies could be used and provide benefits even if irrigation fluidis not utilized in the ablation electrode assemblies. All directionalreferences (e.g., upper, lower, upward, downward, left, right, leftward,rightward, top, bottom, above, below, vertical, horizontal, clockwise,and counterclockwise) are only used for identification purposes to aidthe reader's understanding of the present disclosure, and do not createlimitations, particularly as to the position, orientation, or use of thedisclosure. Joinder references (e.g., attached, coupled, connected, andthe like) are to be construed broadly and can include intermediatemembers between a connection of elements and relative movement betweenelements. As such, joinder references do not necessarily infer that twoelements are directly connected and in fixed relation to each other. Itis intended that all matter contained in the above description or shownin the accompanying drawings shall be interpreted as illustrative onlyand not limiting. Changes in detail or structure can be made withoutdeparting from the spirit of the disclosure as defined in the appendedclaims.

What is claimed is:
 1. An ablation electrode assembly comprising: aninner core member having a distal end, a proximal end, and alongitudinal axis, wherein the inner core member comprises a thermalinsulator having a reduced thermal conductivity; and an outer shellsurrounding at least a portion of the inner core member, the outer shellhaving a distal end and a proximal end, wherein the outer shellcomprises an electrically conductive material; wherein the inner coremember includes a plurality of channels located on an outer surface ofthe inner core member; wherein each of the plurality of channelsincludes a thermal sensor disposed therein; and wherein the inner coremember and the outer shell define a non-irrigated space therebetweenconfigured to interrupt or reduce a heat transfer path between thethermal sensors.
 2. The ablation electrode assembly of claim 1, whereinthe inner core member and the outer shell define a space therebetweenconfigured to interrupt or reduce a heat transfer path between thethermal sensors disposed in each of the plurality of channels.
 3. Theablation electrode assembly of claim 2, wherein the space is annular. 4.The ablation electrode assembly of claim 2, where the space comprises avacuum or evacuated region.
 5. The ablation electrode assembly of claim1, wherein the inner core member comprises: an inner surface defining aninner cavity, and a radially extending passageway, relative to thelongitudinal axis of the inner core member, that extends from the innercavity to the outer surface of the inner core member.
 6. The ablationelectrode assembly of claim 1, wherein the inner core member furthercomprises an axially extending passageway, relative to the longitudinalaxis of the inner core member, extending from an inner cavity of theinner core member to the distal end of the inner core member.
 7. Theablation electrode assembly of claim 1, wherein the outer shell isscored with a plurality of axially extending slots, relative to thelongitudinal axis of the inner core member, to separate the outer shellinto a plurality of segments.